1. Field of the Invention
The present invention relates to an information processing apparatus on which a contact type image sensor for use in an image reader, a facsimile machine or the like is mounted. More particularly, the present invention relates to an improvement in the composition of parts of the above-described contact type image sensor.
2. Related Background Art
FIG. 1A is a schematic side elevational view which illustrates a conventional contact type image sensor. FIG. 1B is a partial enlarged view of the same. FIG. 2 is a schematic structural view which illustrates the image sensor mounted on the body of the apparatus. As shown in FIGS. 1 and 2, the conventional contact type image sensor is arranged in such a manner that one hollow portion 50 is created by a frame 51, a reading glass 52, a bottom plate 53, side plates 54 and the like. Furthermore, optical elements, such as an LED array 55, a SELFOC lens 56 and a sensor substrate 57, are accommodated in the above-described hollow portion 50.
However, in the above-described conventional structure, the leading portions of screws 58 for use in assembling the elements undesirable appear in the hollow portion 50 in which the optical elements are accommodated. Therefore, chips 59 genenerated in a tap portion at the time of tightening the screw 58 are undesirably introduced into the above-described hollow portion 50. As a result, the chips 59 will adhere to the open side of the lens, the reverse side of the reading glass and the surfaces of the sensor devices and the like and thereby the image is adversely critically influenced. The above-described problem becomes seriously in a case where the contact type image sensor has an improved reading resolution because a small chip will adversely affect the quality of the formed image.
The oxidation and optically adverse influence upon the frame 51 have been prevented by applying a black insulating material to the surface of the frame 51 after the frame 51 has been formed into the final shape. Therefore, no electrical connection has not been established between the above-described frame 51 and the bottom plate 53 and the side plates 54 which accommodate the optical elements.
As a result, although the above-described bottom plate 53 and the side plates 54 are disposed to surround the above-described frame 51, the force to shield electric waves becomes insufficient and an undesirable antenna effect is generated, causing the following problems to take place in a case where the contact type image sensor is, as described above, mounted on an apparatus such as an image reader.
That is, it is difficult, for the structure composed of the frame 51, the bottom plate 53 and the side plates 54 to confine the electric waves which have been generated in the sensor substrate 57 when the contact type image sensor is operated. As a result, the radiant noise characteristics will be deteriorated because the electric waves can easily leak outside. Because of the same reason, the force to shield the electric waves made incident from the external portion of the contact type image sensor is insufficient. Therefore, the contact type image sensor cannot be operated stably. In order to overcome the above-described problems, it might be feasible to employ a structure arranged in such a manner that a large quantity of the ground wires are used or an electric wave shield tape is used. However, the overall cost will be enlarged excessively in this case.
The above-described problems become more seriously in a case where the regulation of radiant noise, which has been intensified recently, must be met or when the apparatus is arranged to adapt to the electric waves the frequency of which has been raised or strengthened and to take a measurement against the deterioration in the resistance against external noise which will be taken place when the speed of the operational clock of the contact type image sensor is raised in order to improve the reading resolution and to raise the reading speed.
Furthermore, since the LED array 55, which is the heat generation source, is usually disposed adjacent to the central portion of the frame 51, it is difficult to satisfactorily discharge the accumulated inside heat.
It becomes more difficult to overcome the above-described problem of the heat radiation in a case of a small apparatus. Furthermore, if the reading resolution of a document reading apparatus is desired to be improved or its speed is intended to be raised, a strong light source must be used, causing a serious problem to arise in that the calorific power is excessively enlarged.